Term diseconomies of scale Definition: Increasing long-run average cost that occurs as a firm increases all inputs and expands its scale of production. This is graphically illustrated by a positively-sloped long-run average cost curve and typically occurs for relatively large levels of production. Diseconomies of scale overwhelm by economies of scale for relatively large production levels. Together, economies of scale and diseconomies of scale cause the long-run average cost curve to be U-shaped.